In what was another miserable night for the Knights, they would ultimately fall to the Broncos by 36 points to 12 while also losing Bradman Best to a dislocated elbow - with the hope no fracture was sustained in the gruesome injury.
After being locked at six points all at halftime, and just two points behind - 14-12 - after 61 minutes, the Knights would let in 22 unanswered points during the final 20 minutes of the game.
The loss has left the Knights sitting in 14th place on the competition table with just three wins from 11 games, and with finals hopes rapidly disappearing.
The Broncos, on the other hand, have moved into the top four for the time being on the back of their fifth straight victory.
The Knights had every right to feel aggravated by decisions though, with the returning Dane Gagai denied a try in the first half after appearing to regain control of a football he had bobbled before Selwyn Cobbo scored a try in the second half which started the rot of unanswered points on the back of what looked like a clear obstruction.
O'Brien said he couldn't understand why Cobbo's try was allowed to stand.
"I think if that happens on the 10 metre line or on the tryline, the rule should be the same all the way down the field," O'Brien said.
"I don't understand it. If that had happened down there (on the tryline), it would have been pulled back, I imagine."
Despite the decisions, O'Brien said his team shutting off was inexcusable.
"Because that happened, it's inexcusable for us to sort of turn it up there (at the end)," he said.
"I get that it took a bit of wind out of the sails."
The loss for Newcastle, which was also Anthony Milford's first in a Newcastle jumper, has left O'Brien facing further questions and pressure with the New Zealand Warriors awaiting in Redcliffe next week.